Using CO2 Efflux Rates to Indicate Below-Ground Growing Seasons by Land-use Treatment

CO₂ efflux rates are affected by vegetation type, temperature, and soil surface conditions, and serve as an indicator of the length of the below-ground biological and microbial growing season. This study determined the effect of three land-use treatments on CO₂ efflux and growing season lengths in Southeast Virginia on two forested mineral soil wetlands. CO₂ efflux, soil temperature, and soil moisture were measured 24 times in 18 months at plots representing forest, early successional field, and bare ground land-use treatments. CO₂ efflux differed (p < 0.05) by treatment in the order forest > field > bare ground. CO₂ efflux was higher in hardwood- than conifer-dominated forest and higher in bare ground plots that were not inundated. Appreciable CO₂ efflux took place even once leaves had fallen off deciduous trees, and most of the CO₂ efflux appeared to be from vegetation rather than microbial sources during that period. Variability in CO₂ efflux was best described by the interaction between soil temperature and soil moisture (R² = 0.32) (p < 0.05). The below-ground growing season indicated by appreciable CO₂ efflux was similar to that indicated by soil temperatures above 5°C measured at 50 cm, the regulatory reference depth. The CO₂ efflux growing season was 365 days in the forest but was 9–16 days shorter in the field and 21–78 days shorter in the bare ground land-use treatment plots. These data can be used to modify the regulatory growing season definition in forested thermic wetlands and to reflect the environmental variation caused by different land uses.     

Population dynamics of the annual halophyte Spergularia marina on a Baltic seashore meadow

The population dynamics of the annual Spergularia marina was studied during four years on three different sites on a Baltic seashore meadow. The population density varied significantly both between years and between sites. At one of the sites the average population density was higher than at the two other sites. Both differences in reproductive capacity and in density-independent mortality caused differences in population size. Variation in population seed yield or loss of seed or both, between years, to a large extent determined the variation in the population density between years.     

Ecosystem Recovery Across a Chronosequence of Restored Wetlands in the Platte River Valley

Wet meadows in the Platte River valley (PRV) consist of linear wetlands in mesic prairie matrix systems that have been degraded and diminished for agriculture. Restoration in this region is a widespread practice that involves land contouring and seeding native species, however ecosystem recovery following restoration has never been examined. We quantified recovery trajectories and rates of above- and belowground plant biomass, soil physical and chemical properties, and C and N pools in a chronosequence of six restored wet meadows in relation to three natural wetlands. Within each site, we sampled sloughs (deeper habitats) and adjacent margins (slightly higher elevation) for three consecutive years. Varying hydrologic regimes between habitats resulted in differential patterns in ecosystem measurements (bulk density, C mineralization) in both natural and restored wetlands. Total aboveground biomass (TAB), root biomass, root C and N storage, total soil C and N, microbial N, and extractable N increased with years restored in both margins and sloughs. The model predicted rates of increase did not differ between habitats, but elevations of linear regressions were higher in sloughs than margins for root N, total soil C, total soil N, MBN, and extractable total N (P < 0.05). Our results suggest that bulk density and soil organic matter (SOM) represent two useful, easily measured indices of ecosystem recovery, because they were correlated with many pools and fluxes of C and N. Furthermore, we conclude that most change in ecosystem structure and function during the first decade following restoration occurs in shallow soil depths, and ecosystem recovery varies with subtle differences in elevation and associated plant community structure.     

Landscape‐scale redistribution of a highly mobile threatened species,Pteropus conspicillatus (Chiroptera,Pteropodidae), in response to Tropical Cyclone Larry

Abstract Severe category 4 Tropical Cyclone Larry, which crossed north‐east Queensland on 20 March 2006, provided a unique opportunity to examine the short‐term impacts of a major disturbance event on the population of a highly mobile threatened species, Pteropus conspicillatus. As we had recorded, the species’ population distribution in colonial roosts (camps) across the region each month for almost 2 years prior to Cyclone Larry, we continued monthly surveying of P. conspicillatus camp‐sites for a year post‐cyclone. Here we report on how P. conspicillatus responded and redistributed immediately after the cyclone, and over the subsequent year. Post‐cyclone, P. conspicillatus typically roosted in smaller camps than pre‐cyclone, suggesting that these animals had largely dispersed to locate available blossoms and fruit. For 6 months after Cyclone Larry, up to 90% of the pre‐cyclone P. conspicillatus population (ca. 250 000) was unaccounted for across the region. Information provided by the general public assisted us in locating six small camps of P. conspicillatus at ‘new’ locations, but contributed little to increase our overall population estimate for the species at this time. After November 2006, the number of P. conspicillatus built up at located camp‐sites until a post‐cyclone peak of 209 000 at the end of the study in March 2007, comparable with the population estimates in March 2005 and 2006. There is no evidence that the cyclone caused significant direct mortality among P. conspicillatus, although there may yet be longer‐term and indirect effects on population size. We suggest that redistribution by P. conspicillatus makes sense ecologically in the face of major habitat disturbance and short‐ to long‐term food resource limitation, and is not unlike the response of other Australian mainland Pteropus species to seasonal changes in food availability.     

Structure,productivity and energy flow in an alpine grassland in the Garhwal Himalaya

Abstract. Structure, primary production and energy flow were studied in ungrazed and grazed alpine meadows in the Garhwal Himalaya, India. In grazed grasslands, the cover of graminoids increased, the biomass of palatable species was reduced by about 50%, but the biomass of unpalatable species increased, due to reduced competition from the better-foraged species. Generally, 32% of live shoot and root biomass was consumed during a growing season. Also, above-ground plant productivity increased as a result of plant regrowth, while below-ground productivity decreased. Flow and storage of energy in ungrazed and grazed alpine grasslands showed an accumulation of 10.1 and 8.5 kJ/yr with energy conversion efficiencies of 0.7 and 0.6% respectively. Ca. 46% of the net energy accumulated was consumed by herbivores on the grazed grassland. Only 26% of the net captured energy disappeared from the system in the growing season, mainly via root and litter decomposition.